Amplitude modulation system



Dec; 16, '1947. e. M. BROWN 2,432,720

AMPLITUDE MODULATION SYSTEM Filed June 28; 1945- a CW SOIIHLE L i Inventor:

Gebrge M. Brown,

Patented Dec. 16, 1947 2,432,720 AMPLITUDE MODULATION SYSTEM George M. Brown, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York 2 Application June 28, 1945, Serial No. 601,950

14 Claims.

- My invention, relates to amplitude modulation systems, and more particularly to means for offecting amplitude modulation of electromagnetic oscillationsby simultaneous control of a plurality of amplifier tube parameters.

In certain applications where considerable amplifier output is required but only limited modulator output is available, neither plate nor cathode amplifier modulation alone is entirely satisfactory. For example, with simple cathode modulation, it is difficult to obtain high power output at high percentage modulation because it is necessary to reduce the excitation and power output of the amplifier tube far below its normal level in order to obtain high percentage modulation in the positive direction. On the other hand, high modulator power output is necessary to provide a high percentage modulation by plate or plate and screen modulation alone.

Accordingly, it is a general object of my invention to provide a new and improved amplitude modulation system.

It is a further object of my invention to provide new and improved means for obtaining a high percentage carrier wave amplitude modulation with low modulator power output.

It is a still further object of my invention to provide new and improved means for combining the modulation of a plurality of amplifier tube Parameters.

It is a more specific object of my invention to provide single means for introducing into both the anode and cathode circuits of an. amplifier tube suitable modulating potentials derived from a source of signal frequency oscillations.

My invention will be more fully understood and its various 91601 5 and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying'drawing, the single figure of which is a schematic circuit diagram of an amplitude modulation system embodying my invention Referring now to the drawing, 1 have shown an electron discharge device I connected as an amplifier and comprising an anode 2, a cathode 3, a control electrode 4 and a screen electrode 5 The anode 2 is connected to a suitable source-of unidirectional potential supply B+ through an anode circuit comprising a resonant output circuit 6 and a coupling or modulating impedance 1, the impedance 1 being interposed inseries between the supply source and the circuit 6-. The cathode 3 is connected to ground through a cathode biasing resistor 8.. The resonant output cir- 2 cuit 6 is connected to an antenna 9 through a coupling capacitor ID.

The control electrode 4 is connected through a coupling capacitor II to a source l2 of high frequency carrier wave oscillations and is biased negative with respect to the cathode 3 by connection to ground through a grid resistor l3 and a high frequency choke coil I4. The cathode 3 is maintained at ground potential for high irequency osc llations through a by-pass capacitor I5 shunting the cathode resistor 8, The coupling impedance 1 and the positive potential source 13-}- are shunted to ground for high frequencies through a by-pass capacitor [6. The screen grid 5 is connected to positive potential source 3-?- through resistor 28 andcoupling impedance '1, It is also maintained substantially at ground poten tial for high freguencies by connection to the cathode 3' through a by-pass capacitor H.

The amplitude of high frequency oscillations in the discharge device I is modulated by the action of a second electron discharge device I8 having an anode IS, a cathode 2!}, a control electrode 2| and ascreen electrode 22'. The anode I9 is connected to the positive potential sourceB+ through the coupling impedance 1, and the cathode 20' is connected to ground through the cathode resistor 8. The control electrode 21 is connected to a suitable source of signal frequency potential 23 and is biased negatively with respect to the cathode 20 by connection through a grid resistor 24 to a suitable source of grid bias potential 25. It will be understood by those skilled in the art that the bias potential source 25 may maintain the control electrode 2| either positive or negative with re spect to the cathode 2U. Byway of illustration only, I have shown a source of negative bias potential. The screen electrode '22 is maintained positive with respect to the cathode 30 by connection through a resistor 26 to the positive potential source B+ and is maintained at ground potential for signal frequencies" by connection to ground through a lily-pass capacitor 21,

In operation, the discharge device i functions essentially as a class C amplifier to establish in its discharge circuit high frequency oscillations at the frequency of the source H. The amplifier dis--' charge circuit comprise the tuned output circuit 6 and the Icy-pass capacitors and It. The impedance I servesas a signal frequency choke coil. Amplitude modulation of the high frequency oscillations in accordance with the signal potential is effected by operation of the modulator tube [8; The discharge device l8 establishes in its discharge circuit oscillations at signal frequency;

The modulator discharge circuit includes the coupling impedance 7 and the cathode resistor B in the anode and cathode circuits, respectively, of the amplifier l. The modulator tube current traversing the coupling impedance 1 sets up across this impedance a signal frequency potential which serves to modulatev the effective anode potential supplied to .theamplifier device I. Simultaneously, the modulator tube current traversing the cathode resistor 8 establishes across that resistor a grid bias potential modulated at signal frequency, thereby further to facilitate the modulating action of the discharge device I. It will be noted also that, by reason of the connection of the screen grid 5 to the modulator anode l3 through the resistor 28, the signal frequency potential appearing across the coupling impedance 1 serves also to modulate the positive potential of the screen electrode 5. Thus, amplitude modulation of the high frequency oscillations in the resonant output circuit 6 is effected by combined control of three amplifier tube parameters, the modulator tube l8 being connected simultaneously to modulate the amplifier anode voltage, cathode bias, and screen potential.

While I have shown and described only a preferred embodiment of my invention by Way of iilustration, many modifications Will occur to those skilled in the art and I therefore Wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, an electron discharge device having an anode circuit and a control electrode circuit, said circuits having a common cathode portion, a source of high frequency carrier Wave oscillations coupled to said control electrode circuit, a source of signal frequency oscillations, means having impedance at signal frequencies in both said anode circuit and in said common portion, and means for simultaneously impressing oscillations from said second source upon both said impedance means, thereby to introduce into each of said circuits a function of said signal frequency oscillations.

2. In combination, an electron discharge device having an anode circuit and a control electrode circuit, said circuits having a, common cathode portion, a source of high frequency carrier Wave oscillations coupled to said control electrode circuit, a source of signal frequency oscillations, first and second impedance elements in said anode circuit and common portion respectively, and means responsive to said signal frequency oscillations si multaneously to develop a signal frequency modulating potential across said first element and a signal frequency biasing potential across said second element.

3. In combination, a source of high frequency carrier wave oscillations, an electron discharge device having a control electrode circuit coupled to said source and an anode circuit including a coupling impedance, a cathode resistor connected in both said circuits, a second electron discharge device having a control electrode and an anode circuit including said impedance and said resistor, a source of signal frequency oscillations, means for impressing said signal frequency oscillations on the control electrode of said second discharge device thereby to impress across said impedance and said resistor signal frequency modulating and biasing potentials respectively.

4. In combination, a source of high frequency carrier wave oscillations, an electron discharge device having a control electrode circuit coupled to said source and an anode circuit including a coupling impedance and a resonant output circuit in series circuit relation, a cathode biasing resistor common to said circuits, a second electron discharge device having a control electrode and an output circuit including said coupling impedance and said cathode resistor, and means for impressing signal frequency oscillations upon the control electrode of said second discharge device thereby to modulate said high frequency oscillations.

5. In combination, a source of high frequency carrier Wave oscillations, an electron discharge device having a control electrode circuit coupled to said source and an anode circuit including a resonant output circuit and a coupling impedance, a cathode resistor common to said circuits, means maintaining the control electrode of said device at substantially zero bias potential, a second electron discharge device having an anode circuit including said coupling impedance and said cathode resistor, and means including a source of signal frequency oscillations for controlling the anode current in said second discharge device thereby to modulate said high frequency oscillations at signal frequency,

6. In combination, a source of high frequency oscillations, an electron discharge device having a control electrode circuit coupled to said sou ce, an anode circuit for said discharge device serially including a resonant output circuit, a coupling impedance and also a cathode resistor common to said circuits, a second electron discharge device having an output circuit including said impedance and said resistor, and means for controllng the current in said second discharge device thereby to modulate said high frequency oscillations.

'7. In combination, a pair of electron discharge devices having anodes, cathodes and control electrodes, anode circuits for said devices both including a common coupling impedance and common cathode resistor, control electrode circuits for said devices both including said common resistor, the anode circuit of one of said devices including also a resonant output circuit, a source of high frequency oscillations coupled to the control electrode circuit of said one discharge device, and a source of signal frequency oscillations coupled to the control electrode circuit of the other discharge device thereby to modulate the high frequency oscillations in said output circuit.

8. In combination, an electron discharge device having an anode circuit and a control electrode circuit, a source of high frequency carrier wave oscillations coupled to said control electrode circuit, said anode circuit including a source of positive unidirectional potential connected to said an ode through a signal frequency choke coil and connected to said cathode through a cathode biasing resistor common to said circuits, and means including a second electron discharge device for superposing upon both said high frequency choke coil and said cathode resistor signal frequency potentials, thereby to modulate the amplitude of high frequency oscillations in said first discharge device.

9. In combination, a source of high frequency oscillations, an electron discharge device having a control electrode circuit coupled to said source, an anode circuit for said discharge device including a resonant output circuit and a coupling impedance, a cathode bias impedance for said discharge device common to said circuits, a second electron discharge device having an output circuit including both said impedances, and means for controlling the current in said second discharge device thereby to modulate said high frequency oscillations.

10. In combination, an electron discharge device having an anode circuit energized for the transmission of high frequency carrier wave oscillations, a source of signal frequency oscillations, said anode circuit including means providing impedance at the frequency of said source both between its anode and ground and between its cathode and ground, a second electron discharge device energized from said signal source, and means to impress the output of said second discharge device on said anode and cathode in opposite phase with respect to ground thereby to modulate the amplitude of said carrier wave oscillations by said signal frequency oscillations.

11. In combination, an electron discharge device having an anode circuit including a coupling impedance and a common cathode impedance, said device being energized for the transmission of high frequency carrier wave oscillations, a second electron discharge device having an anode circuit also including said coupling and cathode impedances, and a source of signal frequency oscillations coupled to the input of said second device, thereby to impress across said impedances signal frequency modulating potentials.

12. In combination, a source of high frequency carrier oscillations, a source of signal frequency oscillations, an electron discharge device including a cathode, control electrode, screen electrode and anode, an input circuit coupled to said first source and including a connection from said control electrode to a reference point output and screen electrode circuits including connections from said anode and screen electrode respectively to said point, and a common cathode connection from said cathode to said point, each of said connections including substantial impedance at signal frequencies, and means for simultaneously impressing oscillations from said second source upon said anode and screen electrodes in one phase and upon said cathode in opposite phase with respect to said point.

13. In combination, a source of high frequency carrier Wave oscillations, a source of modulation frequency oscillations, an electron discharge device having an anode, cathode and at least a pair of control electrodes, an anode circuit including a coupling impedance and a common cathode bias impedance, a control electrode circuit coupling said first source to one of said electrodes and including said cathode impedance, a second electron discharge device having an input circuit coupled to said second source and an anode circuit including both said impedances, whereby anode current variations at modulation frequencies in said second device are impressed upon said anode and said one control electrode of said first device, and means for additionally impressing said variations upon the other of said control electrodes.

14. In combination, a source of high frequency carrier wave oscillations, a source of signal frequency oscillations, an electron discharge device having an anode, a cathode and a control electrode, an input circuit coupled to said first source and including a connection from said control electrode to a reference point, an output circuit including a connection from said anode to said point, and a connection common to said circuits from said cathode to said point, each of said connections including means having impedance at signal frequencies, and means for simultaneously impressing oscillations from said second source upon said anode in one phase and upon said cathode in opposite phase with respect to said point.

' GEORGE M. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,860,897 Meade May 31, 1932 2,219,449 Hofer et al. Oct, 29, 1940 OTHER REFERENCES A Crystal-Controlled Pack Transmitter, Communications for February 1938, pages 18 and 19. 

